Lead frame and semiconductor device having the same as well as method of resin-molding the same

ABSTRACT

A lead frame structure includes: at least a die pad for mounting a semiconductor chip thereon; a plurality of suspension members mechanically connected with the die pad; and a plurality of supporting members. Each supporting member has a connection region mechanically connected with each of the plurality of suspension members for mechanically supporting the at least die pad via the plurality of suspension pins. The connection region of the supporting member has a penetrating opening portion which provides a mechanical flexibility to the connection region and which allows the connection region to be deformed toward the suspension member upon application of a tensile stress to the suspension member in a down-set process.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lead frame and a semiconductor devicehaving the same as well as a method of resin-molding the same.

All of patents, patent applications, patent publications, scientificarticles and the like, which will hereinafter be cited or identified inthe present application, will, hereby, be incorporated by references intheir entirety in order to describe more fully the state of the art, towhich the present invention pertains.

2. Description of the Related Art

In recent years, the importance of the high density packaging techniquefor realizing an ultra-high density integration of the semiconductordevice has been on the increase. In case that the semiconductor chip hasa single transistor such as a power transistor, it is important tomounting a heat radiator onto the semiconductor device, even a possiblereduction of the cost of the semiconductor device is strongly required.In order to satisfy both requirements for the heat radiation and thecost reduction, a “down-set” was proposed, wherein each die pad of thelead frame is depressed down or set down, so that the die pad has alower level than the other part of the lead frame, and the semiconductorchip is thus mounted on this down-set die pad. The semiconductor devicemounted on the down-set die pad is then resin-molded, wherein a bottomsurface of the down-set die pad is exposed or shown from the bottom ofthe molding resin, so that the down set-die pad serves as a heatradiator or a heat radiation channel.

The down-set process for the die pad causes a variety of mechanicalstress to the die pad, suspension pins and frame portions. In case, thismechanical stress may cause a disconnection of one or more suspensionpins and/or any undesirable deformation of the frame portions.

Japanese laid-open patent publication No. 5-315499 discloses aconventional lead frame structure designed for avoiding any undesireddeformation due to the down-set process. FIG. 1 is a schematicfragmentary plan view of a conventional lead frame structure designedfor avoiding any undesired deformation due to the down-set processdisclosed in Japanese laid-open patent publication No. 5-315499. A leadframe 101 has double frames 102 extending in parallel to each other. Aplurality of die pad 103 is aligned between the double frames 102 and ina direction parallel to the extension direction of the double frames102. Each the die pad 103 is mechanically connected through a pair ofsuspension pins 104 to the frames 102. Namely, the suspension pins 104are thus positioned inside of the frames 102 and opposite outsides ofthe die pad 103 so as to provide a mechanical connection between theeach die pad 104 and the frames 102. The each die pad 103 is alsosurrounded by a set of plural leads 105 which provide electricalconnections through bonding wires to a semiconductor chip not shownwhich is mounted on the die pad 103.

The each semiconductor chip is mounted on the each die pad 103, wherethe die pad 103 is depressed by a die, whereby the level of the die pad103 becomes lower than the frames 102. This process for level-down ofthe die pad 103 is so called to as “down-set”. This down-set of the diepad 103 causes a certain increase in a distance in three-dimensionalspace between the die pad 103 and the frames 102. This amount ofincrease of the distance depends on the amount of the level down.

In accordance with this conventional technique, the suspension pins 104are modified for responding to variation in the distance between the diepad 103 and the frames 102 upon the down-set process. FIG. 2 is afragmentary plan view of a pair of the modified suspension pins forproviding a mechanical connection with a flexibility in distance betweenthe die pad and the frames included in the lead frame of FIG. 1. Each ofthe paired suspension pins 104 has a zigzag shaped portion 104 a in planview. This zigzag shaped portion provides a certain mechanicalflexibility which allows a limited variation in the distance between thedie pad 103 and the frames 102 upon the down-set process. Thismechanical flexibility absorbs or relax a certain mechanical stressapplied to the suspension pins 104 due to variation in the distancebetween the die pad 103 and the frames 102 upon the down-set process.This mechanical flexibility also makes it easy to accomplish thedown-set process. For those reasons, the zigzag shaped portion may alsoserve as a mechanical stress absorption portion.

FIG. 3 is a cross sectional elevation view of the down-set die padconnected through the modified suspension pins to the frames in FIG. 1.In the down-set process, the die pad 103 is depressed by the press ofthe die and becomes level-down by a depth “D” from the flames 102, whilehaving a horizontal distance “T” remain unchanged, wherein the zigzagshaped portions 104 a of the suspension pins 104 are elasticallydeformed to show a stretch or an extension by an increase in thedistance between the die pad 103 and the flames 102. After the die isreleased or removed from the state of pressing the die pad 103, thezigzag shaped portions 104 a still remain stretched to providesubstantially no mechanical stress to the flames 102. Namely, the zigzagshaped portions 104 a make the flames 102 free from any undesireddeformation in connection of the down-set process. The zigzag shapedportions 104 a also make the suspension pins 104 free from a possibledisconnection involved in the down-set process.

Consequently, the zigzag shaped portions 104 a provide such both adesired mechanical flexibility and a mechanical stress absorption as toallow the down set process to make the die pad 103 become level-downfrom the flames 102 by the depth “D”, while having the horizontaldistance “T” remain unchanged, without causing any undesired deformationof the flames 102 and any disconnection of the suspension pins 104. Asshown in FIG. 3, the horizontal distance “T” is defined in a horizontaldirection perpendicular to the longitudinal direction, along which thedouble frames 102 extend.

Japanese laid-open patent publication No. 5-267539 also disclosesanother conventional lead frame structure designed for avoiding anyundesired deformation due to the down-set process. The disclosedtechnical concept in connection with the counter-measure to the down-setprocess is substantially equivalent to the above-described conventionaltechnique. A lead frame has a modified support bar which acts as asuspension pin for supporting a stage which acts as a die pad. Themodified support bar has a stretchable s stress absorber portion whichmay exhibit substantially similar function as the above-described zigzagshaped portions, but which are structurally different from them. Thestretchable s stress absorber portion comprises an annular portionconnected to the support bar and a cross sectional portion.

Returning back to the issue of heat radiation, a heat radiationtechnique is important for mounting a power transistor such as MOSFET,MESFET or bipolar transistor, particularly for a vertical type MOSFETwith a larger current in operation.

In parallel to the above requirement for improvement in the heatradiation structure, a possible shrinking technique of the semiconductordevice or a possible increase in the packaging density of the powertransistors with the lead frame are also important in view of a possiblecost reduction and a possible size-down of an electron device, on whichthe semiconductor devices are mounted.

The present inventor confirmed the following facts. A highly stretchablematerial for the suspension pin is effective to avoid a possibledisconnection of the suspension pin in the down-set process, but whichis insufficient in hardness for the lead frame. Namely, the realizationof the practically using lead frame needs sufficient hardness not onlyto the frames but also the suspension pins. If the suspension pin has anincreased hardness, then this may cause another problem with undesirablelimitation to the necessary stretchability and may allow a frequency ofdisconnection of the suspension pins. For those reasons, simpledependence upon selection of any stretchable material for the suspensionpins are still engaged with any problems described above.

Further, as shown in FIGS. 2 and 3, the above-described conventionalmodified suspension pin 104 has the zigzag-shaped stretchable portion104 a which gives rise to a certain increase in the length size of thesuspension pin 104. The horizontal size “T” should be sufficiently largewith reference to the depth “D”. Ensuring the sufficiently largehorizontal size “T” of the suspension pin 104 makes it difficult torealize a desired increase in the packaging density.

As shown in FIG. 2, the size of the die pad is defined by subtraction ofa double of the horizontal size of the suspension pin 104 from thehorizontal distance between the paired frames 102. Increase in thehorizontal size “T” of the suspension pin 104, while fixing thehorizontal distance between the paired frames 102 would give rise to acertain decrease in the size of the die pad which provides a possibleoccupied area for the semiconductor device to be mounted on the die pad103. The decrease in the size of the die pad results in a decrease inthe packaging density of the semiconductor device. The decrease in thepackaging density make it difficult to realize a desired shrinkage ofthe semiconductor device. Further the increase in the size of the leadframe makes it difficult to achieve an appreciable cost reduction.

A further important issue for manufacturing the semiconductor device ishow to improve the return on investment. It will be preferable as anexample for improving the return on investment that the same dies arecommonly used for semiconductor packages of different types, forexample, down-set free package, down-set packages with various depths indown set. In accordance with the above-described prior art, however, thenecessary minimum length of the suspension pin would depend on thedown-set, and also the depth of the down-set. For this reason, the priorart does not allow the desired common use of the same dies for adown-set variety of the semiconductor packages the prior art isunsuitable for improving the return on investment.

In the above circumstances, the development of a novel lead framestructure free from the above problems is desirable.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a novellead frame structure free from the above problems.

It is a further object of the present invention to provide a novel leadframe structure suitable for down-set with realizing a desired highpackaging density.

It is a still further object of the present invention to provide a novellead frame structure suitable for down-set with allowing a desired highshrinkage of the semiconductor device.

It is yet a further object of the present invention to provide a novellead frame structure suitable for down-set free from any undesired costincrease.

It is yet a further object of the present invention to provide a novellead frame structure suitable for down-set free from any undesiredappearance of disconnection of suspension pin and application ofmechanical stress to frame portions.

It is further more object of the present invention to provide a novellead frame structure suitable for down-set and also heat radiation.

It is moreover object of the present invention to provide a novel leadframe structure suitable for down-set and also return on the investment.

It is another object of the present invention to provide a novelsemiconductor device having an improved lead frame structure free fromthe above problems.

It is further another object of the present invention to provide a novelsemiconductor device having an improved lead frame structure suitablefor down-set with realizing a desired high packaging density.

It is still further another object of the present invention to provide anovel semiconductor device having an improved lead frame structuresuitable for down-set with allowing a desired high shrinkage of thesemiconductor device.

It is yet further another object of the present invention to provide anovel semiconductor device having an improved lead frame structuresuitable for down-set free from any undesired cost increase.

It is still more object of the present invention to provide a novelsemiconductor device having an improved lead frame structure suitablefor down-set free from any undesired appearance of disconnection ofsuspension pin and application of mechanical stress to frame portions.

It is further more object of the present invention to provide a novelsemiconductor device having an improved lead frame structure suitablefor down-set and also heat radiation.

It is moreover object of the present invention to provide a novelsemiconductor device having an improved lead frame structure suitablefor down-set and also return on the investment.

It is an additional object of the present invention to provide a novelmethod of packaging a semiconductor device having an improved lead framestructure free from the above problems.

It is a further additional object of the present invention to provide anovel method of packaging a semiconductor device having an improved leadframe structure suitable for down-set with realizing a desired highpackaging density.

It is a still further additional object of the present invention toprovide a novel method of packaging a semiconductor device having animproved lead frame structure suitable for down-set with allowing adesired high shrinkage of the semiconductor device.

It is yet a further additional object of the present invention toprovide a novel method of packaging a semiconductor device having animproved lead frame structure suitable for down-set free from anyundesired cost increase.

It is still more additional object of the present invention to provide anovel method of packaging a semiconductor device having an improved leadframe structure suitable for down-set free from any undesired appearanceof disconnection of suspension pin and application of mechanical stressto frame portions.

It is further more additional object of the present invention to providea novel method of packaging a semiconductor device having an improvedlead frame structure suitable for down-set and also heat radiation.

It is moreover additional object of the present invention to provide anovel method of packaging a semiconductor device having an improved leadframe structure suitable for down-set and also return on the investment.

The present invention provides a lead frame structure including: atleast a die pad for mounting a semiconductor chip thereon; a pluralityof suspension members mechanically connected with the die pad; aplurality of supporting members, each having a connection regionmechanically connected with each of the plurality of suspension membersfor mechanically supporting the at least die pad via the plurality ofsuspension pins, wherein the connection region of the supporting memberhas a penetrating opening portion which provides a mechanicalflexibility to the connection region and which allows the connectionregion to be deformed toward the suspension member upon application of atensile stress to the suspension member.

The above and other objects, features and advantages of the presentinvention will be apparent from the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments according to the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a fragmentary plan view of a conventional lead frame structuredesigned for avoiding any undesired deformation due to the down-setprocess.

FIG. 2 is a fragmentary plan view of a pair of the modified suspensionpins for providing a mechanical connection with a flexibility indistance between the die pad and the frames included in the lead frameof FIG. 1.

FIG. 3 is a cross sectional elevation view of the down-set die padconnected through the modified suspension pins to the frames in FIG. 1.

FIG. 4A is a schematic fragmentary plan view of a first typicalstructure before down-set of a lead frame in a first embodimentaccording to the present invention.

FIG. 4B is a cross sectional elevation view, taken along an X1-X2 lineof FIG. 4A.

FIG. 4C is a schematic fragmentary plan view of the first typicalstructure after down-set of the lead frame of FIG. 4A.

FIG. 4D is a cross sectional elevation view, taken along the X1-X2 lineof FIG. 4C.

FIG. 5A is a schematic fragmentary plan view of a second typicalstructure before down-set of a lead frame in a second embodimentaccording to the present invention.

FIG. 5B is a cross sectional elevation view, taken along a Y1-Y2 line ofFIG. 5A.

FIG. 5C is a schematic fragmentary plan view of the second typicalstructure after down-set of the lead frame of FIG. 5A.

FIG. 5D is a cross sectional elevation view, taken along the Y1-Y2 lineof FIG. 5C.

FIG. 6 is a fragmentary perspective view of a tapered end region with anopen-type notch of each of connection bars of a lead frame of FIG. 5A.

FIG. 7A is a schematic fragmentary plan view of a third typicalstructure after down-set of a lead frame in a third embodiment accordingto the present invention.

FIG. 7B is a cross sectional elevation view, taken along a Z1-Z2 line ofFIG. 7A.

FIG. 8 is a fragmentary cross sectional elevation view of a down-set diepad mounted with a semiconductor chip and placed in a resin-molding die.

FIG. 9 is a cross sectional elevation view of a semiconductor packageformed in accordance with the novel method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first aspect of the present invention is a lead frame structureincluding: at least a die pad for mounting a semiconductor chip thereon;a plurality of suspension members mechanically connected with the diepad; a plurality of supporting members, each having a connection regionmechanically connected with each of the plurality of suspension membersfor mechanically supporting the at least die pad via the plurality ofsuspension pins, wherein the connection region of the supporting memberhas a penetrating opening portion which provides a mechanicalflexibility to the connection region and which allows the connectionregion to be deformed toward the suspension member upon application of atensile stress to the suspension member.

It is preferable one typical example that the penetrating openingportion comprises a single slender-shaped continuously extending openingportion which extends along a longitudinal center axis of the supportingmember.

It is further preferable one typical example that the singleslender-shaped continuously extending opening portion comprises a slithaving opposite closed ends.

It is also preferable as one typical example that the singleslender-shaped continuously extending opening portion comprises anopen-type notch having an open end and an opposite closed end. Further,the opposite closed end may advantageously have a generallycircle-shape.

It is also preferable as one typical example that the penetratingopening portion comprises a single circle-shaped opening portion.

It is also preferable as one typical example that the penetratingopening portion comprises a single oval-shaped opening portion.

It is also preferable as one typical example that the connection regionhas at least an tapered side-edge which retracts from the suspensionmember as a position becomes closer to the suspension member.

A second aspect of the present invention is a lead frame structure asdown-set including: at least a die pad with a semiconductor chip mountedthereon; a plurality of suspension members mechanically connected withthe die pad; a plurality of supporting members, each having a connectionregion mechanically connected with each of the plurality of suspensionmembers for mechanically supporting the at least die pad via theplurality of suspension members, and the plurality of supporting membershaving a higher level than the at least die pad, wherein the connectionregion of the supporting member has a deformed penetrating openingportion toward the suspension member as applied with a tensile stress tothe suspension pin in a state of the lead frame as down-set.

It is preferable as one typical example that the penetrating openingportion comprises a single slender-shaped continuously extending openingportion which extends along a longitudinal center axis of the supportingmember.

It is also preferable as one typical example that the singleslender-shaped continuously extending opening portion comprises a slithaving opposite closed ends.

It is also preferable as one typical example that the singleslender-shaped continuously extending opening portion comprises anopen-type notch having an open end and an opposite closed end.

It is also preferable as one typical example that the opposite closedend has a generally circle-shape.

It is also preferable as one typical example that the penetratingopening portion comprises a single circle-shaped opening portion.

It is also preferable as one typical example that the penetratingopening portion comprises a single oval-shaped opening portion.

It is also preferable as one typical example that the connection regionhas at least a straight side-edge deformed from such a tapered side-edgeas having retracted from the suspension member as a position becomescloser to the suspension member.

A third aspect of the present invention is a semiconductor packageincluding: a die pad: a semiconductor chip mounted on the die pad; aplurality of suspension members mechanically connected with the die pad,and the plurality of suspension members extend outwardly and upwardlyfrom the die pad; and a molding resin embedding the plurality ofsuspension members and the semiconductor chip, while a bottom surface ofthe die pad is shown from the molding resin.

A fourth aspect of the present invention is a method of resin-molding asemiconductor chip. The method comprises the following steps. A leadframe is prepared and placed which includes: at least a die pad formounting a semiconductor chip thereon; a plurality of suspension membersmechanically connected with the die pad; and a plurality of supportingmembers. Each supporting member has a connection region mechanicallyconnected with each of the plurality of suspension members formechanically supporting the at least die pad via the plurality ofsuspension pins. The connection region of the supporting member furtherhas a penetrating opening portion. At least a semiconductor chip is thenmounted on the at least die pad. The lead frame with the semiconductorchip is then down-set on an inner wall of a bottom resin-molding die,wherein a bottom surface of the die pad is made into contact with theinner wall of the bottom resin-molding die. The penetrating openingportion provides a mechanical flexibility to the connection region andallows the connection region to be deformed toward the suspension memberupon application of a tensile stress to the suspension member. A resininjection process is then carried out for resin-molding thesemiconductor chip on the die pad to form a resin-molded semiconductorpackage. Finally, the resin-molded semiconductor package is releasedfrom the lead frame.

It is preferable as one typical example that the penetrating openingportion comprises a single slender-shaped continuously extending openingportion which extends along a longitudinal center axis of the supportingmember. Further, the single slender-shaped continuously extendingopening portion may advantageously comprise a slit having oppositeclosed ends.

It is also preferable as one typical example that the singleslender-shaped continuously extending opening portion comprises anopen-type notch having an open end and an opposite closed end. Further,the opposite closed end may advantageously have a generallycircle-shape.

It is also preferable as one typical example that the penetratingopening portion comprises a single circle-shaped opening portion.

It is also preferable as one typical example that the penetratingopening portion comprises a single oval-shaped opening portion.

It is also preferable as one typical example that the connection regionhas a tapered side-edge retracting from the suspension member as aposition becomes closer to the suspension member prior to the down-setprocess.

The following embodiments are typical examples for practicing theforegoing aspects of the present invention. Although the subject mattersof the present invention have been described in details, the followingadditional descriptions in one or more typical preferred embodiments orexamples will be made with reference to the drawings for making it easyto understand the typical modes for practicing the foregoing aspects ofthe present invention.

First Embodiment

A first embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 4A is a schematicfragmentary plan view of a first typical structure before down-set of alead frame in a first embodiment according to the present invention.FIG. 4B is a cross sectional elevation view, taken along an X1-X2 lineof FIG. 4A. FIG. 4C is a schematic fragmentary plan view of the firsttypical structure after down-set of the lead frame of FIG. 4A. FIG. 4Dis a cross sectional elevation view, taken along the X1-X2 line of FIG.4C.

A lead frame 1 has a pair of tie bars 2 which extend in parallel to eachother in a first horizontal direction. A die pad 3 is mechanicallyconnected through a pair of suspension pins 4 to the paired tie bars 2.The lead frame 1 may optionally and advantageously be made of a metal oran alloy, preferably copper alloys, or iron-nickel alloy. One typicalexample of the thickness of the lead frame 1 may be, but not limited to,approximately 0.15 mm.

Further, the selected region of the each tie bar 2 in the vicinity ofthe suspension pin 4 has a slit 5 which has a slender shape with alongitudinal direction parallel to the extension direction of the tiebar 2 and also perpendicular to a center line of the suspension pin 4.The slit 5 may, for example, comprise a single slender-shapedcontinuously extending opening portion. One typical example of the widthof the slit 5 may be identical or approximately similar to the thicknessof the lead frame 1, for example, may be, but not limited to the rangeof 0.15 mm through 0.2 mm. One typical example of the longitudinallength of the slit 5 may be identical or approximately similar to about10 times of it's width, for example, may be, but not limited to therange of 1.5 mm through 2.0 mm. The longitudinal length of the slit 5may typically be greater than the length of the suspension pin 4.

The each tie bar 2 has a tapered region 6 which is adjacent to aconnection portion to the suspension pin 4, so that a width of the eachtie bar 2 proportionally decreases toward the center axis of thesuspension pin 4. The tapered region 6 includes the above-describedselected region having the slit 5.

In accordance with this first typical embodiment of the presentinvention, the above-described slit 5 and the tapered region 6 areimportant for the down-set process to be described below. This leadframe 1 may be formed by press working and may be flat-shape as shown inFIG. 4B.

This flat-shape lead frame 1 as shown in FIGS. 4A and 4B is thensubjected to the down-set process using the known dies. The down-setprocess may be carried out as follows. The tie bars 2 shown in FIGS. 4Aand 4B are fixed by stopper. The die pad 3 is sandwiched by a punch anda die to apply a tensile stress to the suspension pins 4. This tensilestress causes the tapered region 6 with the slit 5 to show suchrespective deformations as shown in FIGS. 4C and 4D. The presence of theslit 5 or the deformations of the tapered region 6 with the slit 5 allowthe die pad 3 to show level down from the tie bars 2 by a depth “D” eventhe suspension pins 4 show a slight stretch. Namely, the deformed slitSa has a larger width as shown in FIGS. 4C and 4D as compared to theoriginal shape of the slit 5 shown in FIGS. 4A and 4B. The combinationof the above-described tapered shape end region 6 toward the center andthe slit 5 provides a desired flexibility without application of anexcess mechanical tensile stress to the suspension pins 4, whereby thedown-set of the die pad 3 can be realized without any possibility of thedisconnection of the suspension pins 4.

Further, as shown in FIG. 4C, the deformation of the slit 5 causes thetapered region 6 to have a straight and not-tapered inside edge which isimportant for the resin-molding process to be described below. Thedeformation of the tapered region 6 into the straight and not-taperedinside edges allows a highly accurate resin molding, and ensures thatthe tie bars 2 are free from the undesired resin molding, thereby makingit easy to cut the suspension pins 4 to release the semiconductorpackage from the lead frame 1, wherein the semiconductor chip is mountedon the die pad 3 and resin-molded, while the bottom surface of the diepad 3 is shown from the molding resin.

As shown in FIG. 4D, the combination of the above-described taperedshape end region 6 toward the center and the slit 5 also allows taking alarge ratio of the down-set depth “D” with reference to the horizontalsize “T” of the suspension pin 4 in the down-set state. This means thatthe combination of the above-described tapered shape end region 6 towardthe center and the slit 5 allows taking a large ratio of the down-setdepth “D” with reference to the length size of the suspension pin 4. Thehorizontal size “T” may, for example, be in the range of “1 t” to “2 t”,wherein “t” is the thickness of the lead frame 1, while the down-setdepth “D” may, for example, be “4 t” or larger.

For example, if the thickness of the lead frame is 0.15 mm, then thecombination of the above-described tapered shape end region 6 toward thecenter and the slit 5 allows that the down-set depth “D” is set atapproximately 0.7 mm, while the horizontal size “T” is set atapproximately 0.20 mm.

In contrast to the present invention, the above-described prior artneeds a larger horizontal size “T” of not less than approximately 1.0 mmfor the same down-set depth “D” of approximately 0.7 mm and the samethickness of 0.15 mm, otherwise resulting in a possible disconnection ofthe suspension pin.

Accordingly, the combination of the above-described tapered shape endregion 6 toward the center and the slit 5 allows taking a large ratio ofthe down-set depth “D” to the horizontal size “T”, thereby making itpossible to decrease or reduce the necessary minimum length size of thesuspension pin 4. This makes it possible to increase the occupied areaof the die pad 3 in the lead frame 1. This would give rise to increasethe occupied area of the semiconductor chip as packaged, and thusincrease the packaging density of the semiconductor device. The increaseof the occupied area of the die pad 3 increases the die pad exposedsurface area which defines the heat radiation area, to improve theefficiency of the heat radiation from the semiconductor chip through thedie pad 3. The increase in the packaging density causes the size down orthe shrinkage of the semiconductor package. This also makes it easy toreduce the manufacturing cost of the semiconductor package.

In this embodiment, the slit 5 may be replaceable by any otherpenetrating opening with a variety of its shape in plan view, such as acircle or an oval, provided that the penetrating opening should beformed in the tapered region 6 in the vicinity of the connection pointto the suspension pin 4. For this reason, the above-described slit 5should be interpreted to be one or more penetrating opening which isformed in the tapered region 6 in the vicinity of the connection pointto the suspension pin 4, wherein the one or more penetrating opening mayallow deformations thereof and the tapered shape region, so as to causethe tapered shape region to have a straight and not-tapered inside edge.

Second Embodiment

A second embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 5A is a schematicfragmentary plan view of a second typical structure before down-set of alead frame in a second embodiment according to the present invention.FIG. 5B is a cross sectional elevation view, taken along a Y1-Y2 line ofFIG. 5A. FIG. 5C is a schematic fragmentary plan view of the secondtypical structure after down-set of the lead frame of FIG. 5A. FIG. 5Dis a cross sectional elevation view, taken along the Y1-Y2 line of FIG.5C.

A lead frame 7 has a plurality of die pads 3, which of which ismechanically connected through a pair of suspension pins 4 to adjacenttwo of plural connection bars 8, so that the each die pad 3 ismechanically supported via the paired suspension pins 4 by the adjacenttwo of plural connection bars 8. The plural die pads 3 are aligned in afirst horizontal direction. The each connection bar 8 has a tapered endregion 6 which is connected via adjacent two of the suspension pins 4 toadjacent two of the aligned die pads 3. The each connection bar 8extends in a second horizontal direction perpendicular to the firsthorizontal direction, while the adjacent two of the suspension pins 4extend from the tapered end region 6 in the first horizontal directionto the adjacent two of the die pads 3. Adjacent two of the connectionbars 8 extend in anti-parallel directions to each other but parallel tothe second horizontal direction.

The tapered end region 6 also has an open-type notch 9 which has aslender shape and extends from the end of the tapered end region 6 inthe second horizontal direction along a longitudinal center axis of theeach connection bar 8. The open-type notch 9 has an open end and anopposite closed end. The open-type notch 9 divides the tapered endregion 6 into two divided tapered parts 6 which are respectivelyconnected via the adjacent two suspension pins 4 to the adjacent two diepads 3.

In accordance with this second typical embodiment of the presentinvention, the above-described open-type notch 9 and the tapered region6 are important for the down-set process to be described below. Thislead frame 7 may be formed by press working and may be flat-shape asshown in FIG. 5B. The lead frame 7 may optionally and advantageously bemade of a metal or an alloy, preferably copper alloys, or iron-nickelalloy.

This flat-shape lead frame 7 as shown in FIGS. 5A and 5B is thensubjected to the down-set process using the known dies. The down-setprocess may be carried out as follows. The connection bars 8 shown inFIGS. 5A and 5B are fixed by stopper. The die pad 3 is sandwiched by apunch and a die to apply a tensile stress to the suspension pins 4. Thistensile stress causes the tapered regions 6 with the notches 9 to showsuch respective deformations as opened, shown in FIGS. 5C and 5D. Thepresence of the open-type notch 9 or the deformations of the taperedregion 6 with the open-type notch 9 allow the die pad 3 to show leveldown from the connection bars 8 by a depth even the suspension pins 4show a slight stretch. Namely, the deformed open-type notch 9 a has alarger width as shown in FIGS. 5C and 5D as compared to the originalshape of the open-type notch 9 shown in FIGS. 5A and 5B. The combinationof the above-described tapered shape end region 6 toward the end and theopen-type notch 9 provides a desired flexibility without application ofan excess mechanical tensile stress to the suspension pins 4, wherebythe down-set of the die pad 3 can be realized without any possibility ofthe disconnection of the suspension pins 4.

Further, as shown in FIG. 5C, the deformation of the open-type notch 9causes the tapered region 6 to have straight and not-tapered both-sideedges which are important for the resin-molding process to be describedbelow. The deformation of the tapered region 6 into the straight andnot-tapered inside edges allows a highly accurate resin molding, andensures that the connection bars 8 are free from the undesired resinmolding, thereby making it easy to cut the suspension pins 4 to releasethe semiconductor package from the lead frame 7, wherein thesemiconductor chip is mounted on the die pad 3 and resin-molded, whilethe bottom surface of the die pad 3 is shown from the molding resin.

As shown in FIG. 5D, the combination of the above-described taperedshape end region 6 toward the end and the open-type notch 9 also allowstaking a large ratio of the down-set depth with reference to thehorizontal size in the first horizontal direction of the suspension pin4 in the down-set state. This means that the combination of theabove-described tapered shape end region 6 toward the end and theopen-type notch 9 allows taking a large ratio of the down-set depth withreference to the length size of the suspension pin 4.

The tapered shape end region 6 with the open-type notch 9 of the eachconnection bar 8 will be described in detail with reference to FIG. 6.The open-type notch 9 comprises a straight slender band region extendingfrom the end of the each connection bar 8 along the longitudinal centeraxis and terminated or closed with a circle-shape termination region 10.The down-set process applies tensile stresses to the adjacent suspensionpins 4 in the anti-parallel directions to each other but in parallel tothe second horizontal direction as described above. This application ofthe tensile stress causes the open-type notch 9 to open widely, so thatthe tapered side edges 6 become straight and parallel to the secondhorizontal direction.

It is assumed that the thickness of the connection bar 8 is “t”, a widthof the straight slender band region of the open-type notch 9 represents“W”, and a length of the open-type notch 9 represents “L”. An typicalpreferred example of the size or dimension of the open-type notch 9 wasconfirmed by the present inventor as follows. The width “W” ispreferably in the range of “t” to “2 t”, while the length “L” ispreferably in the range of “5 t” to “10 t”. Further, it was confirmedthat the circle-shape termination region 10 provides a high flexibilityto the opening degree of the open-type notch 9 in the down-set process.This high flexibility may avoid an undesired formation of a gap betweena bottom surface of the die pad 3 and an inner wall of the bottom die,and ensures that the bottom surface of the die pad 3 is shown from thebottom of the semiconductor package.

Accordingly, the combination of the above-described tapered shape endregion 6 and the open-type notch 9 allows taking a large ratio of thedown-set depth to the horizontal size of the suspension pin 4, therebymaking it possible to decrease or reduce the necessary minimum lengthsize of the suspension pin 4. This makes it possible to increase theoccupied area of the die pad 3 in the lead frame 7. This would give riseto increase the occupied area of the semiconductor chip as packaged, andthus increase the packaging density of the semiconductor device. Theincrease of the occupied area of the die pad 3 increases the die padexposed surface area which defines the heat radiation area, to improvethe efficiency of the heat radiation from the semiconductor chip throughthe die pad 3. The increase in the packaging density causes the sizedown or the shrinkage of the semiconductor package. This also makes iteasy to reduce the manufacturing cost of the semiconductor package.

Third Embodiment

A third embodiment according to the present invention will be describedin detail with reference to the drawings. FIG. 7A is a schematicfragmentary plan view of a third typical structure after down-set of alead frame in a third embodiment according to the present invention.FIG. 7B is a cross sectional elevation view, taken along a Z1-Z2 line ofFIG. 7A.

A lead frame 11 has a plurality of die pads 13, which of which ismechanically connected through a pair of suspension pins 14 to taperedend regions of adjacent two of plural connection bars 12, so that theeach die pad 13 is mechanically supported via the paired suspension pins14 by the adjacent two of plural connection bars 12. The each connectionbar 12 extends in a second horizontal direction perpendicular to a firsthorizontal direction, while the each suspension pin 14 extends from thetapered end region of the each connection bar 12 in the first horizontaldirection to the die pad 13. Adjacent two of the connection bars 12extend in anti-parallel directions to each other but parallel to thesecond horizontal direction.

The tapered end region 6 also has an open-type notch 15 which has aslender shape and extends from the end of the tapered end region in thesecond horizontal direction along a longitudinal center axis of the eachconnection bar 12. The open-type notch 15 has an open end and anopposite closed end. The open-type notch 15 divides the tapered endregion into two divided tapered parts.

In accordance with this third typical embodiment of the presentinvention, the above-described open-type notch 15 and the tapered regionare important for the down-set process to be described below. This leadframe 11 may be formed by press working and may be flat-shape, butthereafter the flat shaped lead frame is then subjected to the down-setprocess and the die pad 13 becomes level down as shown in FIG. 7B. Thelead frame 11 may optionally and advantageously be made of a metal or analloy, preferably copper alloys, or iron-nickel alloy. The down-setprocess may be carried out similarly to what has been described in thesecond embodiment. The tensile stress applied to the suspension pins 14causes the tapered regions with the notches 15 to show such respectivedeformations as opened, shown in FIG. 7A. The presence of the open-typenotch 15 or the deformations of the tapered region 6 with the open-typenotch 15 allow the die pad 13 to show level down from the connectionbars 12 by a depth even the suspension pins 14 show a slight stretch.Namely, the deformed open-type notch 15 a has a larger width as shown inFIG. 7A. The combination of the above-described tapered shape end regionand the open-type notch 15 provides a desired flexibility withoutapplication of an excess mechanical tensile stress to the suspensionpins 14, whereby the down-set of the die pad 13 can be realized withoutany possibility of the disconnection of the suspension pins 14.

As shown in FIG. 7A, the combination of the above-described taperedshape end region and the open-type notch 15 also allows taking a largeratio of the down-set depth with reference to the horizontal size in thefirst horizontal direction of the suspension pin 14 in the down-setstate. This means that the combination of the above-described taperedshape end region and the open-type notch 15 allows taking a large ratioof the down-set depth with reference to the length size of thesuspension pin 14.

Similarly to the above-described second embodiment, the open-type notch15 comprises a straight slender band region extending from the end ofthe each connection bar 12 along the longitudinal center axis andterminated or closed with a circle-shape termination region. Thedown-set process applies tensile stresses to the adjacent suspensionpins 14 in the anti-parallel directions to each other but in parallel tothe third horizontal direction as described above. This application ofthe tensile stress causes the open-type notch 15 to open widely, so thatthe tapered side edges become straight and parallel to the thirdhorizontal direction. The circle-shape termination region provides ahigh flexibility to the opening degree of the open-type notch 15 in thedown-set process. This high flexibility may avoid an undesired formationof a gap between a bottom surface of the die pad 13 and an inner wall ofthe bottom die, and ensures that the bottom surface of the die pad 13 isshown from the bottom of the semiconductor package.

Further, as shown in FIG. 7A, plural drain leads 16 are provided whichare directly connected and united with the each die pad 13, wherein thedrain leads 16 extend from a first side of the each die pad 13 and inparallel to the second horizontal direction. A gate lead 17 and pluralsource leads 18 are also provided which are indirectly connected viabonding wires 20 to a gate electrode pad and source electrode pads of asemiconductor chip 19 mounted on the each die pad 13, wherein the gatelead 17 and the plural source leads 18 extend from an opposite secondside of the each die pad 13 and in parallel to the second horizontaldirection.

FIG. 8 is a fragmentary cross sectional elevation view of a down-set diepad mounted with a semiconductor chip and placed in a resin-molding die.The die pad 13 mounted with the semiconductor chip 19 is pressed to aninner bottom wall of a resin-molding die 22. The inner bottom wall has astep-like sectioned shape with a step level difference “D0”. It shouldbe noted that the step level difference “D0” of the inner bottom wall ofa resin-molding die 22 is designed to be smaller than the intendeddown-set depth “D”.

An injection of a molding resin into the molding dies is carried outwith keeping the die pad 13 pressed to the inner bottom wall of theresin-molding die 22. Since the step level difference “D0” of the innerbottom wall of a resin-molding die 22 is smaller than the intendeddown-set depth “D”, then no gap is formed between the bottom surface ofthe die pad 13 and the inner bottom wall of the resin-molding die 22.For example, the step level difference “D0” may be smaller by aboutseveral tens micrometers than the intended down-set depth “D”.

Further, the above-described circle-shape termination region 10 providesa high flexibility to the opening degree of the open-type notch 15 inthe down-set process. This high flexibility may avoid an undesiredformation of a gap between a bottom surface of the die pad 13 and aninner wall of the bottom die, and ensures that the bottom surface of thedie pad 13 is shown from the bottom of the semiconductor package.

Further, as shown in FIG. 7A, the deformation of the open-type notch 15causes the tapered region 6 to have straight and not-tapered both-sideedges which are important for the resin-molding process to be describedbelow. The deformation of the tapered region into the straight andnot-tapered inside edges allows a highly accurate resin molding, andensures that the connection bars 12 are free from the undesired resinmolding, thereby making it easy to cut the suspension pins 14 to releasea semiconductor package 24 from the lead frame 11, wherein thesemiconductor chip 19 is mounted on the die pad 13 and resin-molded witha resin 23, while the bottom surface of the die pad 13 is shown from themolding resin 23 as shown in FIG. 9.

Accordingly, the combination of the above-described tapered shape endregion and the open-type notch 15 allows taking a large ratio of thedown-set depth to the horizontal size of the suspension pin 14, therebymaking it possible to decrease or reduce the necessary minimum lengthsize of the suspension pin 14. This makes it possible to increase theoccupied area of the die pad 13 in the lead frame 11. This would giverise to increase the occupied area of the semiconductor chip aspackaged, and thus increase the packaging density of the semiconductordevice. The increase of the occupied area of the die pad 13 increasesthe die pad exposed surface area which defines the heat radiation area,to improve the efficiency of the heat radiation from the semiconductorchip through the die pad 13. The increase in the packaging densitycauses the size down or the shrinkage of the semiconductor package. Thisalso makes it easy to reduce the manufacturing cost of the semiconductorpackage.

In accordance with this third embodiment, the suspension pins have beencut for no longer use as leads, but in order to release thesemiconductor package 24 from the lead frame 11. It is, however,possible to apply the novel lead frame of the present invention to theother case, wherein the long suspension pins are provided withoutcutting the same for use of the leads from the semiconductor device.

The present invention is also applicable to a difference case that thesemiconductor chip is mounted on the lead frame free from the down-setprocess for packaging the semiconductor chip with the same resin-moldingdie as shown in FIG. 8. This means that the present invention allows thecommon use of the same resin-molding die for the different types of thelead frames, for example, the down-set lead frame and the down-set-freelead frame. This improves the return on investment.

Although the invention has been described above in connection withseveral preferred embodiments therefor, it will be appreciated thatthose embodiments have been provided solely for illustrating theinvention, and not in a limiting sense. Numerous modifications andsubstitutions of equivalent materials and techniques will be readilyapparent to those skilled in the art after reading the presentapplication, and all such modifications and substitutions are expresslyunderstood to fall within the true scope and spirit of the appendedclaims.

1-3. (canceled).
 4. A lead frame structure, comprising: at least one diepad for mounting a semiconductor chip thereon; a plurality of suspensionmembers mechanically connected to said die pad; and a plurality ofsupporting members each having a connection region mechanicallyconnected with each of said plurality of suspension members formechanically supporting said at least one die pad via said plurality ofsuspension pins; wherein said connection region of said supportingmember has a penetrating opening portion which provides a mechanicalflexibility to said connection region and which allows said connectionregion to be deformed toward said suspension member upon application ofa tensile stress to said suspension member; wherein said penetratingopening portion comprises a single slender-shaped continuously extendingopening portion which extends along a longitudinal center axis of saidsupporting member; and wherein said single slender-shaped continuouslyextending opening portion comprises an open-type notch having an openend and an opposite closed end.
 5. The lead frame structure as claimedin claim 4, wherein said opposite closed end has a generallycircle-shape. 6-11. (canceled).
 12. A lead frame structure, comprising:at least one die pad with a semiconductor chip mounted thereon; aplurality of suspension members mechanically connected to said die pad;and a plurality of supporting members, each having a connection regionmechanically connected to each of said plurality of suspension membersfor mechanically supporting said at least one die pad via said pluralityof suspension members, and said plurality of supporting members having ahigher level than said at least one die pad; wherein said connectionregion of said supporting member has a deformed penetrating openingportion toward said suspension member as applied with a tensile stressto said suspension pin in a state of said lead frame as down-set;wherein said penetrating opening portion comprises a singleslender-shaped continuously extending opening portion which extendsalong a longitudinal center axis of said supporting member; and whereinsaid single slender-shaped continuously extending opening portioncomprises an open-type notch having an open end and an opposite closedend.
 13. The lead frame structure as claimed in claim 12, wherein saidopposite closed end has a generally circle-shape. 14-25. (canceled).